He is credited with the advancement of Dutch astronomy through his scientific contributions of positional measurements, his popularization of astronomy in the Netherlands, and by helping to build a state-of-the-art observatory in 1861 (Today it is known as the "Old Observatory").

The Old Observatory in Leiden

The Old Observatory in 2013, after restoration

He made a series of drawings of Mars at its opposition in 1862 and made a fairly precise determination of its rotational period.